It is old to provide well safety valves, such as disclosed in U.S. Pat. No. 3,782,461 and in co-pending U.S. patent application Ser. No. 027,207, filed Apr. 5, 1979, having a gas chamber for closing the valve and in which the valve is actuated to an open position by hydraulic pressure from the well surface. However, in utilizing such safety valves in extreme deep set applications, the control fluid hydrostatic pressure in the hydraulic flow control line may be in excess of 5,000 psi. While conventional safety valves may be charged to provide a closing pressure greater than 5,000 psi to overcome the existing hydrostatic pressures, excessive friction is created on any seals and the possibility of losing the charged gas, which would cause the valves to fail in the open position, is present.
The present invention is directed to providing a well safety valve which can be utilized at greater depths in wells which can be actuated by small differentials in the hydraulic control lines, and in which the gas in the closing gas chamber is unlikely to escape.